Thermal and Radiation Injuries

Overview & Types - Injury Spectrum

Ocular thermal and radiation injuries result from exposure to extreme temperatures or various forms of radiation, leading to a wide range of damage.

• Thermal Injuries:
  • Flame burns: Direct contact with fire.
  • Scald burns: Hot liquids/steam.
  • Contact burns: Hot objects (e.g., curling irons, molten metal).
  • Electrical burns: Passage of electrical current.
• Radiation Injuries:
  • Ultraviolet (UV) Radiation: Photokeratitis (e.g., welder's flash, snow blindness).
  • Infrared (IR) Radiation: Glassblower's cataract, retinal burns.
  • Ionizing Radiation: (X-rays, gamma rays) Cataract, retinopathy, dry eye.

Injury Spectrum:

• Superficial: Conjunctival hyperemia, corneal epithelial defects.
• Moderate: Stromal edema, uveitis, partial-thickness scleral/corneal burns.
• Severe: Corneal opacification, full-thickness burns, globe perforation, retinal damage, cataract formation, phthisis bulbi.

⭐ UV radiation primarily affects the cornea and conjunctiva, causing photokeratitis, while IR radiation is more associated with cataract formation (glassblower's cataract).

Chemical Burns - Alkali & Acid Attack

• Alkali Burns: More severe (liquefactive necrosis, saponification). E.g., Lime ($Ca(OH)_2$ - common), $NaOH$, $NH_3$. Deeper penetration.
• Acid Burns: Generally less severe (coagulative necrosis). E.g., $H_2SO_4$, $HCl$. ⚠️ HF is an exception (acts like alkali).
• Prognosis: Limbal ischemia (key factor). Grading: Roper-Hall or Dua classification.

  ⭐ Alkali burns are more dangerous due to rapid penetration and saponification of cell membrane lipids.

• Management Principles:
  • Immediate: Copious irrigation (water/RL/NS, ≥ 2L or 30 mins, target pH 7.0-7.4).
  • Medical: Topical steroids (↓inflammation), cycloplegics (↓pain), antibiotics, topical citrate. Systemic: Vitamin C, Doxycycline (anti-collagenase).
  • Surgical: Amniotic membrane transplant (AMT), limbal stem cell transplant (LSCT), keratoplasty.

True Thermal & UV Injuries - Heat & Light Zaps

• Thermal Burns (Heat): Direct tissue coagulation from flame/flash.
  • Eyelids: Erythema, blisters, eschar. Late: ectropion, entropion.
  • Cornea: Epithelial defects, stromal haze, potential perforation.
  • Management: Immediate copious irrigation, topical antibiotics, cycloplegics, lubrication. Amniotic membrane for severe burns.
• UV Keratitis (Photokeratitis/Welder's Flash): UV-B absorption by corneal epithelium.
  • Symptoms: Delayed onset (6-12 hrs), severe pain, photophobia, foreign body sensation, tearing.
  • Signs: Conjunctival injection, diffuse punctate epithelial erosions (PEE) in interpalpebral zone.
  • Management: Cycloplegics, topical NSAIDs, lubrication. Prophylactic antibiotics if large defect. Resolves 24-72 hrs.

  ⭐ UV keratitis classically presents with a 6-12 hour latency period after exposure, with diffuse punctate epithelial erosions on fluorescein staining.

IR & Ionizing Radiation - Deep Damage Rays

• Infrared (IR) Radiation (Longer Wavelengths):
  • Sources: Molten glass/metal, intense sunlight.
  • Mechanism: Thermal; deep tissue heating.
  • Lens: True exfoliation of anterior capsule, "Glassblower's cataract" (PSC).
  • Retina: Macular burns (solar retinopathy).
  • Prevention: IR-protective eyewear.
• Ionizing Radiation (X-rays, Gamma rays):
  • Sources: Radiotherapy, accidental exposure.
  • Mechanism: DNA damage, free radicals; affects dividing cells.
  • Lens: Most radiosensitive. Radiation cataract (PSC).
    • Threshold: 2 Gy (single), 5 Gy (fractionated).
    • Latency: Months to years.
  • Retina: Radiation retinopathy (ischemia, neovascularization).
    • Threshold: 30-35 Gy.
  • Other: Dry eye, keratitis, optic neuropathy.
  • Management: Shielding, dose fractionation, treat complications.

⭐ The lens is the most radiosensitive ocular structure to ionizing radiation; cataracts (PSC) can develop after 2 Gy.

High‑Yield Points - ⚡ Biggest Takeaways

• UV keratitis (photokeratitis): Severe pain, SPK after 6-12 hour latent period (welding, snow blindness).
• Infrared radiation (glassblowers): Classically causes true exfoliation of anterior lens capsule and heat-induced cataract.
• Ionizing radiation (radiotherapy): Can induce delayed radiation retinopathy, cataracts, and severe keratoconjunctivitis sicca (dry eye).
• Thermal eyelid burns: Frequently result in cicatricial ectropion or entropion, leading to exposure keratopathy.
• Corneal thermal burns: Cause immediate coagulative necrosis and opacification; prognosis depends on burn depth and area.